I. Field of the Invention
The present invention relates to an automatic device and to a process for automatically holding up and fixing in position (immobilizing) the parts cut out of a workpiece when a closed path is electroerosively cut in it, as well as an application involving the automatic removal of the cut out parts.
II. Description of the Prior Art
Such a cutting operation is generally performed by means of a tool-electrode constituted by a wire, a band or a thin rod which is approximately vertical. An electric generator causes eroding discharges between the electrode and the workpiece (or blank) which is thus cut by gradual advance of the electrode along a substantially horizontal path. In order to simplify, the term "cut out part" (or "scrap") as used herein will apply to any part separated from a blank during a cutting operation, whether it be a scrap cut-off from the desired piece or, on the contrary, an internal part, which, in itself, constitutes the desired piece the scrap being then comprised of the remainder of the workpiece.
Whenever a profile is cut along a closed line or when its ends come flush with the edge of the workpiece, it ensues that, upon completion of the operation, the scrap part falls off. The disadvantage lies in the fact that the falling motion starts before the end of the operation, when the scrap part is only held by a narrow bridge material whose resistance finally becomes insufficient to sustain the weight of the scrap part. The latter therefore tends to sink crosswise and pinch the wire while the generator is still operating. The electrode wire thus keeps cutting but it is deviated from its ideal course and causes permanent marks on the mechanical surfaces.
The traditional solutions require the involvement of an operator, i.e. to place blocks under the central piece, shortly before the cutting step is completed. This operation cannot be performed at the beginning of the machining operation since the lower machining head would then collide with the blocks during the cutting process.
The blocks may be replaced by fasteners, parallelograms or telescopic forks but all of these devices either require a manual step or are difficult to automate due to their excessive dimensions.
The device disclosed in U.S. Pat. No. 4,484,052 includes a small magnet dispenser for this purpose, attached to the machining head, but this device is cumbersome due to the fact that it has to lay the magnets along a precut slot whose direction varies constantly. Furthermore, in several applications, the material to be cut is copper, aluminum or another nonmagnetic material. Furthermore, the automatic removal of the cut out parts is made very difficult in the presence of magnets.